Single lamp rapid start ballast



Dec. 27, 1966 M. ROSIAK 3,295,015

SINGLE LAMP RAPID START BALLAST Filed Feb. '7, 1964 United States Patent3,295,015 SINGLE LAMP RAPID START BALLAST hiarion Rosiak, MountProspect, IlL, assignor to Advance Transformer Co., Chicago, Ill., acorporation of Illinois Filed Feb. 7, 1964. Ser. No. 343,374 14 Claims.(Cl. 315-239) This invention relates generally to fluorescent lampballasts but more particularly is concerned with a ballast for use witha single fluorescent lamp of the so-called rapid start type.

The rapid start fluorescent lamp differs from the instant startfluorescent lamp in that it has filaments in the envelope ends which areenergized to produce clouds of electrons to aid in starting the lamp ata voltage lower than required for starting the instant start lamp. Itdiffers from the pre-heat start lamp in that its filaments arecontinuously energized, instead of being heated momentarily duringstarting. The rapid start balast, therefore, has filament windingsnormally closely coupled with the primary Winding, to supply thefilament current.

The design of a ballast for a rapid start lamp demands the considerationof at least three aspectsone of which is concerned with requirementswhich give rise to good starting characteristicsthe second of which isconcerned with eificient operationand the third of which is concernedwith requirements of personnel safety. Various regulatory organizationsset the requirements and standards which are to be followed, includingballast manufacturers, organizations, lamp manufacturers,specifications, and safety groups such as the Underwriters Laboratories.

The invention herein is concerned with providing .good starting andoperating characteristics for a rapid start lamp ballast, while meetingthe safety requirements determined as acceptable. This is achieved tosome extent With prior circuits, but according to the invention herein,a novel circuit is provided which is simpler and cheaper than priorcircuit-s, without sacrificing any of the requirements demanded.

The invention will be described in connection with a single lamp ballastfor igniting and operating a 40 watt rapid start lamp, although theconstruction and principles may be applied to rapid start fluorescentlamps of other ratings.

For proper starting of a 40 watt fluorescent rapid start lamp, thevoltage applied at open circuit across the lamp is specified as 227.5volts R.M.S. at 60 cycles. The line voltage is full rated value, whichmay be assumed to be 120 volts A.C. The actual specification is given as90% of rated line voltage at 205 volts R.M.S.

Further, a voltage must exist by capacitive coupling, from one end ofthe lamp to ground, represented by a metal fixture that is grounded,whose peak value must exceed 311 volts at full rated line voltage. Thisis specified as exceeding 280 volts at 90% of rated line voltage.

The achievement of the above R.M.S. and peak voltages do not pose severeproblems in ballast design in and of themselves, but when added to thesafety requirements demanded in ballasts by the UnderwritersLaboratories, for example, considerable expense has resulted in thepast.

If a primary winding is energized such that a filament Winding coupledthereto is heated, it is feasible for a person to hold the fluorescentlamp in one hand and to contact ground completing a circuit through thelamp. If the voltage is suficiently high, the lamp will fire and couldcause shock, burns, or even death. Consequently, the limitation placedupon ballasts for this type of fluorescent lamp calls for a maximumpermissable R.M.S. voltage to ground from any end of the lamp not toexceed 180 volts, and a maximum peak to ground not to Patented Dec. 27,1966 ice R.M.S., volts Peak, volts For starting 227. 5 311 For safety325 All of these values are those existing at full rated line voltage;the starting voltages are the minimum required; the safety voltages arethe maximum permitted.

The only difference between the values mentioned above relative to themanner in which they are measured, is that in the case of the safetyvoltages, these are the values to ground, while in the case of thestarting voltages, the R.M.S. value given is that across the terminalsof the lamp.

The prior circuits which have attacked this problem have taken twoforms. One form uses a pair of so-called disconnect sockets in which theremoval of the primary end of the lamp from its socket will open theprimary winding. The other form of circuit isolates the secondarywinding from the primary winding by a high ohmage resistor with thesecondary winding providing the full open circuit peak voltage and thefull R.M.S. voltage to the fixture.

The primary object of the invention as inferred above, is to provide aballast for use with a rapid start circuit which achieves good startingcharacteristics and meets safety requirements, without the use of eitherdisconnect sockets or isolating resistors. In the first instance,obviating the use of disconnect sockets means that the system into whichthe ballat is connected will be more economical, and thus result insaving for the installer or fixture manufacturer; in the secondinstance, the ballast manufacturer saves the cost and labor ofconnecting a resistor in the ballast circuit and the size of thesecondary winding is smaller.

An important object of the invention is to provide a ballast of thecharacter described in which the peak voltage to ground lies between 311and 325 volts, the R.M.S. voltage across the lamp is over 227.5 volts,and the R.M.S. voltage to ground is less than 180 volts.

One of the common requirements of a fluorescent ballast is to keep thecurrent drawn from the line as close to unity power factor aspracticable, and preferably to have this current on the leading side.The inductive effect of a highly inductive secondary is normally offsetby the use of a series condenser in the secondary circuit. The normalballasts of today are of the high leakage reactance type, andpractically all of these will have one or more condensers in theirsecondary circuits, but this gives rise to lamp currents producingpeaked waves. Such current waves during operation are not conductive tomaximum light output, and one technique for the obviation of such peakwaves has been described in US. Patent 2,461,957 which consists ofproviding a high reluctance gap in the secondary magnetic circuit.

It is believed that the gap prevents saturation of the iron in thevicinity of the secondary winding. The magnetomotive force of themagnetic circuit partially expends itself in the gap and thereby limitsthe magnetic flux to a point where saturation with attendant drop ininductance during those portions of the cycle when the current wave is amaximum does not occur. Mechanical problems make or the provision of acomplete gap difficult, hence the gap in such ballasts is usuallybridged by an iron web or connection to enable the core to be assembledand held together.

In the instant invention, it is desired to have the peaked voltagedescribed above for aid in starting, and this is achieved by the ironportion of the bridge saturating, but it is also desirable to have thegood wave shape during operation. The use of a bridged gap accomplishesboth ends, and in the circuit to be described, the provision of thisstructure comprises an important object of the invention.

Other objects and advantages will occur to those skilled in this art asa description of a preferred embodiment is set forth hereinafter, inconnection with which the drawing illustrating the same should enable acomplete understanding thereof.

In the drawing:

FIG. 1 is a plan view, with portions in section, showing theconstruction of the transformer portion of the invention.

FIG. 2 is a schematic diagram showing the electrical circuit of a systemfor operating a rapid start fluorescent lamp using the invention.

FIG. 3 is a portion of the schematic diagram of FIG. 2 showing amodification of the electrical circuit of the invention.

The objects and advantages of the invention are achieved by providing atransformer having a primary and a secondary winding, connected inauto-transformer relation across a fluorescent lamp, the transformerhaving two taps to enable the desired voltages to be achieved. A bridgedgap in the magnetic circuit of the secondary winding provides a peakvoltage in the secondary winding which is combined with theprimary-induced otherwise sinusoidal voltage in the secondary winding toachieve the peak voltage falling between the desired limits of 311 and325 volts from the end of the lamp to the grounded fixture. It alsoprovides good current wave shape during operation. The RMS. voltage forignition of the lamp is provided by choosing the proper tap on theprimary into which the secondary winding is connected so that there is aportion of the primary winding bucking the secondary winding in itscircuit to ground. About half of the primary winding is used in additiveauto-transformer relationship with the secondary to achieve the desiredends.

Referring now to the drawing, the reference character designates thetransformer portion of a ballast 12 which is shown schematically in FIG.2 by the broken line rectangle. A ballast of this kind has a metalcanister in which the components are immersed in a potting compound.Electrical leads protrude from the canister. The only other component inthe canister 12 besides the transformer is the series condenser 14 and acapacitor bleed resistor usually connected across the condenser andradio interference capacitors which are not shown.

The transformer 10 has a shell type of core formed of stacks of T-shapedand F-shaped laminations, forming a central winding leg 16 and side legs18 held together by clamps 2i) engaging notches 22 formed in the cornersof the side legs. The cross head 24 of the T-shaped central winding leg16 forms the left end magnetic return yoke, and the in-turned ends 26engage the right hand end of the central winding leg on opposite sidesthereof at 28 to form the right end magnetic return yoke. The inwardlydirected extensions 30 that are integral with the side legs 18 arespaced from the central winding leg by means of high reluctancenon-magnetic gaps 32. to provide shunts at 34. The core is preferablystamped in well-known scrapless technique so that the inner edges of theside legs 18 are identical in configuration to the outer edges of thecentral winding leg 16 but spaced therefrom outwardly andlongitudinally. The space produced during stamping by the projections 30results in notches 2-6 on opposite edges of the central winding leg anda necked portion 38.

It will be appreciated that the necked portion 38 is in effect anarrowed cross section of the central winding leg and together with thenotches 36 may be considered a bridged gap. Other constructions of coremay be used with slots or notches or cuts to produce different forms ofbridges or bridged gaps. The desired effect is to provide a peakedvoltage wave on open circuit, in the secondary winding, while at thesame time preventing peaked current waves in the secondary circuitduring operation.

The two pairs of windows 40 and 42 are occupied respectively by theprimary and secondary windings P and S, the windows 4-0 also having thefilament windings F and F mounted therein closely coupled with theprimary winding P.

Looking now at FIG. 2, the primary winding P has the leads 44 and 46 bymeans of which it may be connected to a line such as 120 volts 60 cycleAC. The lead 44 is adapted to be connected to the so-called hot side ofthe line, and the lead 46 is intended to be connected to the groundedside of the line.

The primary is divided into three parts, designated P1, P2 and P3, bymeans of two taps at 43 and 50 and the polarity markings for allwindings indicates that their instantaneous voltage relationship one tothe other is additive along the length of the winding P. The secondaryWinding S has its left terminal connected by the lead 52 to the tap 50and the polarity mark at the left of the Winding S indicates that withrespect to a circuit including the secondary winding S and the primarypart P3 the winding S bucks P3, but with respect to a circuit includingthe secondary winding S and the primary part P2 the winding S adds tothe winding P2.

Filament windings F1 and F2 are connected respectively to the leads54-55 and 56-57 which extend out of the ballast canister. The leads54-55 are adapted to be connected to one filament of a rapid startfluorescent lamp, such as for example the left hand filament of the lampL shown in FIG. 2, while the leads 56-57 are adapted to be connected tothe second filament of the same rapid start fluorescent lamp, forexample the right hand filament of the lamp L, Lamp L is set in afixture which has a grounded metal reflector or plate 58 in closeproximity and capactive coupled relationship to the lamp.

Tap 48 connects by the jumper 60 to the lead 55, and the secondarywinding S connects through the series condenser 14 by way of the lead 62to the lead 56. Note that the winding S and the primary part P2. areconnected in additive auto-transformer relationship at tap 50 (which maybe termed an auto-transformer junction) across the lamp L so that theopen circuit voltage of the secondary winding S which is peaked becauseof the bridged gap 364-8 will have superimposed thereon a virtualsinusoidal voltage produced in the primary. The reason that primary partP1 is not included in this circuit is because its voltage added to thatof the part P2 and the voltage of the secondary winding S is more thanneeded for the open circuit voltage across the lamp. Its presence isneeded for adjustment of the proper characteristics of the transformerwith respect to currents, power and induced voltages. There may becircumstances where the primary parts P1 and P2 may be combined.

The secondary winding is chosen to give the proper step-up voltage andpeaked voltage desirable for starting the lamp L. As explained, for a 40watt rapid start fluorescent lamp the voltage across the lamp forstarting is required to be about 228 volts and in the particular circuitdescribed herein, only the primary part P2 is needed to augment the opencircuit voltage of the secondary winding S. Adjustment of the tap 4Sadjusts the R.M.S. starting voltage.

If one examines the circuit from the grounded lead 46 through the partP3, the auto-transformer junction 50, the secondary winding S and thecondenser 14 through the leads 62 and 56, it will be seen that thevoltage across the intervening space between the lamp and the metalmember 58 is provided by an auto-transformer relation in which thevoltage of P3 is bucking that of S. This is the voltage which a personwould be subjected to if he held the left hand lamp terminals in hishand while the right hand end was connected in circuit, and he touchedthe ground. The maximum R.M.S. permitted for this is 180 volts and inthe structure described it turns out to be somewhat less than that.

The peak voltage needed between the lamp and ground is achieved by thesecondary winding S operating in conjunction with the bridged gap 3638.This peaked voltage occurs on open circuit as a result of the bridgedgap 36-38 being unsaturated at the time that the flux of the primarywinding passes through zero. The voltage induced in S will suddenly riseat this point because the change in flux with respect to time is maximumas it passes through zero, and voltage is proportional to change influx.

The auto-transformer junction 50 provides an easy way of adjusting thepeak voltage, because it subtracts a sinusoidal voltage from thatappearing in the secondary winding. The size of the bridged gap 36-38and the location of the tap or junction 50 provides two parameters whichcan be varied to suit conditions. The total peak voltage from the lampto ground was chosen as one which is less than the 325 volts A.C.considered dangerous by Underwriters Laboratories, and more than 311volts A.C. considered the minimum by lamp and ballast manufacturersstandards for reliable starting of the 40 watt rapid start lamp.

A practical example of a ballast was constructed in accordance with theinvention for igniting and operating a 40 watt T-12 rapid start lampfrom a 120 volt, 60

cycle line. The details of construction of the ballast were as follows:

Inches Total length of the core 4.26 Width of core (assembled) 2.08Width of winding leg .76 Width of windows .31 Width of extensions 30 .19Width of side legs 18 .35 Width of cross head 24 .39 Width of ends 26.39 Length of windows 40 1.58 Length of windows 42 1.72 Length ofextensions 30 .225 Air gaps 32 .085

All of these dimensions are approximate within a few thousandths, exceptfor the last two given. These latter are typical for one construction.An eifort has been made to draw the structure of FIG. 1 to scale. Thestack height was .8 inch, and the laminations were of 24 gauge siliconsteel, although good results would be obtained using cold rolled types.

With respect to the windings and related details, the

following obtained:

Turns A.W. G. wire 6 R.M.S. The open circuit starting voltage across thelamp L from lead 54 to the lead 56 was 246 volts R.M.S.

During operation of the lamp, the line current was 475 ma. and the lampcurrent was 422 ma. the power factor being 97.5. The condenser voltagewas 272 volts.

The ballast operated with good regulation over the range of variationnormally expected in line voltage, and within the temperature rangepermitted for such a device by Underwriters Laboratories requirements.

The construction of the ballast may be varied without sacrificing theadvantages of the invention. As shown in FIG. 3, a condenser 14'conveniently may be located in lead 52 instead of in the lead 62 asshown in FIG. 2. If the peak voltage achieved by means of a given corestructure were low enough to fall in the desired range, there may not beneed for the secondary to be tapped into the primary at 50, but it maybe connected directly to lead 46. Under such circumstances, the tap 48would be the only adjustment for proper open circuit voltage. Variationof air gap and bridged gap dimensions would affect these voltages.

Lamps other than 40 watt T-12 rapid starts would also require somemodifications. None of such changes are believed outside the scope ofthe invention.

What it is desired to secure by Letters Patent of the United States is:

11. A ballast for igniting and thereafter operating a gaseous dischargelamp of the rapid start type from an A.C. power line one side of whichis grounded and the lamp adapted to be mounted adjacent to andcapacitively coupled with a grounded metal member, said ballastcomprising: an elongate magnetic core, a transformer mounted on saidcore and having a primary winding and a secondary winding looselycoupled relative one another, the primary winding having first andsecond end terminals with the lead means for connecting the respectiveend terminals to the ungrounded and grounded sides of said A.C. line,respectively, said primary winding having first and second taps dividingsaid primary winding into three parts with all parts additive within theprimary winding, the first primary part being between the first tap andthe first end terminal, the second primary part being between the firstand second taps, and the third primary part being between the second tapand the second end terminal, the secondary winding being connected inadditive auto-transformer relationship with the second primary part onlyand together therewith having lead means including a series condenserfor connecting the combined second primary part and secondary windingacross the terminals of said lamp, and the secondary winding forming abranch series circuit with the third primary part in which the secondarywinding bucks the third primary part, said core having a bridged gap inthe vicinity of the secondary winding whereby to provide a peakedvoltage wave on open circuit for starting the lamp.

2. A ballast as claimed in claim 1 in which there is a shunt having ahigh reluctance air gap in the core be tween the primary and secondarywindings, the core has a central winding leg and the windings aremounted on the central winding leg, the bridged gap comprises a pair ofopposed notches formed in respective opposite edges of the centralwinding leg with a necked portion therebetween, and the bridged gap isfully enclosed by the secondary winding.

3. A ballast as claimed in claim 1 in which the series condenser has oneterminal thereof connected to one end of the secondary winding, and theother end of the secondary winding is connected to the second tap.

4. A ballast adapted to provide proper igniting voltage for a rapidstart type of fluorescent lamp while providing safe open circuitvoltages when said lamp and ballast are connected to an A.C. source oneside of which is grounded and there is a grounded metallic member in thevicinity of the lamp, which comprises: a transformer having an elongatemetal core with a central winding leg, a primary winding and a secondarywinding disposed on the central winding leg coaxially, but spaced fromone another, a

magnetic shunt including an air gap between the windings, lead means forconnecting the first and second primary winding end terminals to thegrounded and ungrounded sides of the source, respectively, the secondarywinding having one end terminal thereof connected to the primary Windingat an auto-transformer junction proximate to the first end terminal ofthe primary winding, means including a series condenser for extendingconnections from the secondary winding and one part of the primaryWinding on one side of said auto-transformer junction to the terminalsof the lamp with the said one part and secondary winding connected inadditive auto-transformer relation across said lamp, a tap on saidprimary winding between said second end terminal and saidauto-transformer junction forming between said tap and second endterminal another part of said primary winding additive to said one part,said tap being a portion of said means, and there being a bridged gap inthe secondary portion of the metal core.

5. A ballast adapted to be connected to a fluorescent lamp of the rapidstart type and also adapted to be connected to a source of A.C. voltageto ignite and operate the said lamp when connected in a system includingboth the lamp and source, and in which there is a grounded side of thesource and a grounded metal member in the vicinity of the lamp foraiding in starting the lamp, which comprises: an iron core mounting aprimary winding and a secondary winding in loosely coupled voltagestep-up inductive relation, the secondary Winding being connected inadditive auto-transformer relation with one part of said primary Windingto form one circuit, said one circuit having lead means for extendingconnections from said one circuit to the terminals of said lamp wherebyto impress the voltage of said circuit across said lamp When said lampis connected to said lead means, the secondary winding being connectedin subtractive auto-transformer relation with a second part of theprimary winding to form a second circuit, said second circuit having oneterminal commom with one of said lead means and adapted to have a secondterminal for extending a connection to ground, the primary windinghaving a third part which is included in neither of said first andsecond circuits, but is effective to produce flux for linking with thesecondary winding, whereby when said ballast, lamp and source areconnected together, the R.M.S. open circuit voltage from either lampterminal to ground will be substantially lower than the voltage acrossthe lamp.

6. A ballast as claimed in claim in which there is a series condenser inthe said one circuit.

7. A ballast as claimed in claim 6 in which there is magnetic shunt withhigh reluctance gap between the primary and secondary windings toprovide the loose coupling and there is a bridged gap in the magneticcircuit under the secondary winding to produce a peaked starting voltagewhile preventing saturation in the magnetic circuit during operation ofthe lamp.

3. A ballast as claimed in claim 5 in which said primary winding has atleast one tap dividing same into said two parts, and the primary windinghas end terminals for extending connections to said source, the secondpart being electrically adjacent to that end terminal adapted to extendto the grounded side of the source.

9. A lighting system for a fluorescent lamp which includes a fluorescentlamp of the rapid start type arranged to be ignited and operated from asource of AC. voltage having a grounded side and an ungrounded side, andincluding a transformer having a magnetic core, a primary windingmounted on the core and having one end terminal connected to theungrounded side of the source and the second end terminal connected tothe grounded side of the source, a metallic conductor in close proximityto the lamp and connected to ground, a secondary Winding mounted on themagnetic core in step-up inductive lati Wi h and p ated from the primarywinding by a magnetic shunt including an air gap, at least one tap onthe primary winding defining a first primary part between said tap andthe first end terminal and a second primary part between said tap andthe second end terminal, whereby said second primary part is connectedbetween the tap and ground, one terminal of the secondary winding beingconnected to said tap, the end of said first primary part opposite thetap being connected to one terminal of the lamp, the second terminal ofthe secondary winding being connected in series with a condenser andextending to the second terminal of the lamp, the secondary winding andfirst primary part being so connected that their open circuit voltagesadd in the circuit including the lamp and being connected inauto-transformer relation across the lamp by virtue of theirarrangement, the secondary winding being connected in a second circuitin series with the second primary part from the second terminal of thelamp to ground, the secondary winding and secondary part being inbucking relation in said second circuit whereby the total R.M.S. opencircuit voltage from the second terminal to ground will always be lessthan the R.M.S. open circuit voltage across the lamp, the end of thefirst primary part forming a second tap of the primary winding, therebeing a third primary part between said second tap and the said one endterminal the voltage of which is not included in either of saidcircuits, and there being a bridged gap in the magnetic core in thevicinity of the secondary winding to provide a substantially peakedvoltage for starting and a substantially unpeaked current for operatingthe lamp.

it A system as claimed in claim 9 in which the core includes an outershell and an inner central winding leg, the windings are coaxiallymounted end to end on the winding leg, the shunt includes portions ofthe core extending between the shell and winding leg with air gaps inseries with said portions, and the bridged gap is located in the centralWinding leg within the secondary winding and between the ends thereof.

11. A ballast adapted to be connected to a single fluorescent lamp ofthe rapid start type and also adapted to be connected to a source of AC.voltage to ignite and operate the said lamp when connected in a systemincluding both the lamp and source, and in which there is a groundedside of the source and a grounded metal member in the vicinity of thelamp for aiding in starting the lamp, which comprises an iron coremounting a primary winding and a secondary winding in loosely coupledvoltage step-up inductive relation, a tap on the primary dividing theprimary into two parts, the secondary winding being connected inadditive auto-transformer relation with one part and together with saidpart having a pair of leads for extending connections to said lamp, acondenser in series with said secondary winding, one of said leads beingconnected at said tap, the end terminals of said primary winding havingmeans for extending connections therefrom respectively to the source,the said one part being disposed between the tap and that end terminaladapted to be connected to the grounded side of the source, the ironcore having a voltage peak producing structure in the vicinity of thesecondary winding so as to provide a peak to ground voltage from one ofsaid pair of leads to meet starting and safety requirements, while atthe same time having an R.M.S. starting voltage across said pair ofleads substantially greater than the R.M.S. voltage from either toground.

12. A ballast for a single rapid start lamp comprising a primary windingand a secondary winding mounted on an iron core in voltage step-up,loose, inductive relation, a part of the primary being in additiveauto-transformer connection with the secondary and together therewithhaving leads with a series condenser in them for extending connectionsto the lamp, the core having a bridged gap in the secondary partthereof, the primary winding connected across a line, one side of whichis grounded, one end of said one part of said primary being coupled tosaid grounded side of said line, the amount of primary included in saidauto-transformer connection and the turns ratio being chosen such thatthe open circuit R.M.S. voltage across the connections to the lamp ishigher than the safe R.M.S. voltage from one of said connections toground, the peak starting voltage from one of said connections to groundis less than the safe peak voltage to ground and is in excess of theopen circuit R.M.S. voltage by approximately 30%.

13. A ballast as claimed in claim 12 in which the ballast is constructedto ignite and operate a single 40 watt rapid start lamp from a 120 volts60 cycle line, and in which the open circuit R.M.S. voltage across theconnections is at least 227.5 volts, the safe R.M.S. voltage to groundis 10 at most 180 volts, and the peak voltage to ground is between 311and 325 volts.

14. A ballast as claimed in claim 12 in which the primary windingincludes another part coupled between said 5 one part and said groundedside of the line and connected to said secondary winding in buckingrelationship.

References Cited by the Examiner UNITED STATES PATENTS 8/1958 Kayser315-282 2,958,806 11/1960 Lord 315239 X JAMES W. LAWRENCE, PrimaryExaminer.

C. R. CAMPBELL, Assistant Examiner.

1. A BALLAST FOR IGNITING AND THEREAFTER OPERATING A GASEOUS DISCHARGELAMP OF THE RAPID START TYPE FROM AN A.C. POWER LINE ONE SIDE OF WHICHIS GROUNDED AND THE LAMP ADAPTED TO BE MOUNTED ADJACENT TO ANDCAPACITIVELY COUPLED WITH A GROUNDED METAL MEMBER, SAID BALLASTCOMPRISING: AN ELONGATE MAGNETIC CORE, A TRANSFORMER MOUNTED ON SAIDCORE AND HAVING A PRIMARY WINDING AND A SECONDARY WINDING LOOSELYCOUPLED RELATIVE ONE ANOTHER, THE PRIMARY WINDING HAVING FIRST ANDSECOND END TERMINALS WITH THE LEAD MEANS FOR CONNECTING THE RESPECTIVEEND TERMINALS TO THE UNGROUNDED AND GROUNDED SIDES OF SAID A.C. LINE,RESPECTIVELY, SAID PRIMARY WINDING HAVING FIRST AND SECOND TAPS DIVIDINGSAID PRIMARY WINDING INTO THREE PARTS WITH ALL PARTS ADDITIVE WITHIN THEPRIMARY WINDING, THE FIRST PRIMARY PART BEING BETWEEN THE FIRST TAP ANDTHE FIRST END TERMINAL, THE SECOND PRIMARY PART BEING BETWEEN THE FIRSTAND SECOND TAPS, AND THE THIRD PRIMARY PART BEING BETWEEN THE SECOND TAPAND THE SECOND END TERMINAL, THE SECONDARY WINDING BEING CONNECTED INADDITIVE AUTO-TRANSFORMER RELATIONSHIP WITH THE SECOND PRIMARY PART ONLYAND TOGETHER THEREWITH HAVING LEAD MEANS INCLUDING A SERIES CONDENSERFOR CONNECTING THE COMBINED SECOND PRIMARY PART AND SECONDARY WINDINGACROSS THE TERMINALS OF SAID LAMP, AND THE SECONDARY WINDING FORMING ABRANCH SERIES CIRCUIT WITH THE THIRD PRIMARY PART IN WHICH THE SECONDARYWINDING BUCKS THE THIRD PRIMARY PART, SAID CORE HAVING A BRIDGED GAP INTHE VICINITY OF THE SECONDARY WINDING WHEREBY TO PROVIDE A PEAKEDVOLTAGE WAVE ON OPEN CIRCUIT FOR STARTING THE LAMP.